Digital Subscriber Line (DSL) technology, often referred to as “broadband”, is a family of services that provide digital data transmission over the metallic twisted copper pairs that form the telephone lines in a local telephone network. DSL is commonly used to provide a customer's home with a network connection, typically to the Internet via an ISP.
The rate, or speed, of a broadband line depends on a number of factors, including the length of the telephone line over which the service operates, and the general quality of the line. Other factors that affect the rate include external factors such as interference.
Predicting broadband line rates can be a challenge. If a telephone line has had broadband provisioned on it before, then the rate for the previous line can be used as a guide. However, if this is not available, then current methods simply average existing broadband line rates from the same exchange or region. This tends to result in estimates that rarely match the actual outcome. Some techniques are slightly more sophisticated, and group all lines having a similar line characteristic, and the select the minimum rate that say 80% of the lines can reach.
Even though there are clear technical difficulties in estimating the rate of a broadband line, there is still a growing expectancy for line rate predictions to be more accurate and not simply quote some potential (advertising) maximum.